Field emission electron sources, often referred to as field emission materials or field emitters, can be used in a variety of electronic applications, e.g., vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers, and klystrons and in lighting.
Display screens are used in a wide variety of applications such as home and commercial televisions, laptop and desktop computers and indoor and outdoor advertising and information presentations. Flat panel displays can be an inch or less in thickness in contrast to the deep cathode ray tube monitors found on most televisions and desktop computers. Flat panel displays are a necessity for laptop computers, but also provide advantages in weight and size for many of the other applications. Currently laptop computer flat panel displays use liquid crystals, which can be switched from a transparent state to an opaque one by the application of small electrical signals. It is difficult to reliably produce these displays in sizes larger than that suitable for laptop computers.
Plasma displays have been proposed as an alternative to liquid crystal displays. A plasma display uses tiny pixel cells of electrically charged gases to produce an image and requires relatively large electrical power to operate.
Flat panel displays having a cathode using a field emission electron source, i.e., a field emission material or field emitter, and a phosphor capable of emitting light upon bombardment by electrons emitted by the field emitter have been proposed. Such displays have the potential for providing the visual display advantages of the conventional cathode ray tube and the depth, weight and power consumption advantages of the other flat panel displays. U.S. Pat. Nos. 4,857,799 and 5,015,912 disclose matrix-addressed flat panel displays using micro-tip cathodes constructed of tungsten, molybdenum or silicon. WO 94-15352, WO 94-15350 and WO 94-28571 disclose flat panel displays wherein the cathodes have relatively flat emission surfaces.
Field emission has been observed in two kinds of nanotube carbon structures. L. A. Chemozatonskii et al., Chem. Phys. Letters 233, 63 (1995) and Mat. Res. Soc. Symp. Proc. Vol. 359, 99 (1995) have produced films of nanotube carbon structures on various substrates by the electron evaporation of graphite in 10−5–10−6 torr (1.3×10−3–1.3×10−4 Pa). These films consist of aligned tube-like carbon molecules standing next to one another. Two types of tube-like molecules are formed; the A-tubelites whose structure includes single-layer graphite-like tubules forming filaments-bundles 10–30 nm in diameter and the B-tubelites, including mostly multilayer graphite-like tubes 10–30 nm in diameter with conoid or dome-like caps. They report considerable field electron emission from the surface of these structures and attribute it to the high concentration of the field at the nanodimensional tips. B. H. Fishbine et al., Mat. Res. Soc. Symp. Proc. Vol. 359, 93 (1995) discuss experiments and theory directed towards the development of a buckytube (i.e., a carbon nanotube) cold field emitter array cathode. A. G. Rinzler et al., Science 269, 1550 (1995) report the field emission from carbon nanotubes is enhanced when the nanotubes tips are opened by laser evaporation or oxidative etching. W. B. Choi et al., Appl. Phys. Lett. 75, 3129 (1999) and D. S. Chung et al., J. Vac. Sci. Technol. B 18(2) report the fabrication of a 4.5 inch flat panel field display using single-wall carbon nanotubes-organic binders. The single-wall carbon nanotubes were vertically aligned by paste squeezing through a metal mesh, by surface rubbing and/or by conditioning by electric field. They also prepared multi-wall carbon nanotube displays. They note that carbon nanotube field emitters having good uniformity were developed using a slurry squeezing and surface rubbing technique. They found that removing metal powder from the uppermost surface of the emitter and aligning the carbon nanotubes by surface treatment enhanced the emission. Single-wall carbon nanotubes were found to have better emission properties than multi-wall carbon nanotubes but single-wall carbon nanotube films showed less emission stability than multi-wall carbon nanotube films. Zettl et al., U.S. Pat. No. 6,057,637 claim a field emitter material comprising a volume of binder and a volume of BxCyNz nanotubes suspended in the binder, where x, y and z indicate the relative ratios of boron, carbon and nitrogen.
N. M. Rodriguez et al., J. Catal. 144, 93 (1993) and N. M. Rodriguez, J. Mater. Res. 8, 3233 (1993) discuss the growth and properties of carbon fibers produced by the catalytic decomposition of certain hydrocarbons on small metal particles. The U.S. Pat. No. 5,149,584, U.S. Pat. No. 5,413,866, U.S. Pat. No. 5,458,784, U.S. Pat. No. 5,618,875 and U.S. Pat. No. 5,653,951 disclose uses for such fibers.
There is a continuing need for technology enabling the commercial use of acicular carbon in electron field emitters.